1. Field of the Invention
This invention relates generally to wood frame building structures, and more particularly to structures exposed to extreme wind and/or seismic conditions where building codes dictate that these structures be protected against structural failure and/or to save lives of occupants.
Wood structures predominate in residential and light commercial construction, and when wood framing is employed the structure must be protected from upward, shear and overturning loads developed by either wind or seismic activity which differs with geographical location and is enforced by different building codes for these areas. In the case of upward loads, the building is generally tied to the foundation using a variety of steel connectors that tie the bottom plate to the foundation, studs-to-plates, floors-to-walls (in the case of two or more floors), and roof-to-walls. Typically, for uplift, connectors are attached to every stud (16" O.C.), or at least every other stud (32" O.C.). Shear and overturning loads are resisted by a combination of heavy duty steel connectors, (either bolted to, or embedded in, the foundation, and nailed or bolted to the wood frame), and an approved structural sheathing material nailed directly to the exterior of the structure is used to create what is referred to as a "shear wall". The size and number of these steel connectors vary depending on the severity of the wind and/or seismic conditions in the locality of the building, and the building's geometry.
In the United States these connectors are installed during the foundation and framing stages of construction. Connectors and sheathing are generally installed by laborers hired by the framing contractor. Correct size, location and number of fasteners, (nails or bolts), are critical to the required load. Commonly, these laborers are inexperienced which results in improper or inadequate installation. In all structures, locations of connectors mandate their installation during the framing stage due to related components being placed at the same time. This process slows the foundation and framing stages of construction which in turn increases labor costs. Also, existing structures without having these connectors in place are at risk of destruction should a hurricane or earthquake occur.
From the foregoing, it is apparent that there is a critical need for a structural tie-down system that provides for uplift, shear and overturning loads that is cost effective, installed after the foundation and framing stages of the building is complete, and is independent from structural wall sheathing as a integral part of the system.